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St. Cloud’s “Diverging Diamond” – Traffic Safety or $17.5 Million Boondoggle?

9 comments

The Minnesota Department of Transportation (MNDOT) is proposing a radical new interchange design for the St. Cloud area. The St. Cloud Times reports MNDOT will spend $17.5 million to build Minnesota’s first "Diverging Diamond Interchange" to relieve traffic at the busy intersection of Minnesota Highway 15 and County Road 120 near Hennen’s, WalMart and Healthpartners.

The design requires east and west bound traffic lanes to weave to the left of each other on the bridge, and then back. The gets rid of dangerous and time-consuming left turns in front of oncoming traffic by routing all traffic in front of oncoming traffic. The design, first used in France, came to the U.S. when Missouri built one in 2009.

MnDOT’s District 3 project engineer Claudia Dumont acknowledged it will take some time for drivers to get used to the new design. But she’s confident the interchange will improve safety and efficiency.

Converting the entire Highway 15 corridor through St. Cloud to a freeway carries a price tag of more than $300 million, so it’s not likely to happen even in the next 20 to 30 years, Dumont said.

Dumont acknowledged that the new interchange may feel strange at first. Like the roundabouts built in the St. Cloud area recently, “there’s going to be a little bit of a learning curve,” she said.

My partner, Mike Bryant, has written numerous articles about the new roundabouts popping up all over Minnesota, and the resulting problems and issues.

The videos below illustrate the divergent diamond concept, but be forewarned, supporters say looking at it from the air is more confusing than driving through one.

http://www.youtube.com/watch?v=B5JtZMPTNAY

Wow, confusing is right! Here’s one with the freeway over the top:

http://www.youtube.com/watch?v=WF9Cx0pMsbI

Is this better?

http://www.youtube.com/watch?v=c4p-d-6EnOQ

Hopefully the planners are right, and this will reduce car crashes while moving traffic.

9 Comments

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  1. Mike Bryant says:
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    Interesting that compared to a number of other intersections int eh area, we don’t see a lot of collisions at that spot. Like the roundabouts, it’s good to see that the planners continue to look at safety in making these changes. The videos are worth the time to watch.

  2. Joe Crumley says:
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    Thanks.

    Yup, I’ve seen a lot more crashes at the two intersections just south of there (Twelfth St. No. and Eighth St. No./Veteran’s Drive), especially as cars come speeding over the hill and rear-end stopped traffic.

  3. Truckie D says:
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    Interesting post Joe.

    I found this link: http://www.divergingdiamond.com/index.html that discusses this design in detail. Has some good diagrams that clearly illustrate the traffic flow.

    Here are my concerns with this design:

    1. There’s no provision for proceeding back onto the original highway after exiting. Truck drivers often pull off on ramps to check maps, answer calls etc. Also, they sometimes take the wrong exit. With this design, there’s no way to get directly back onto the highway again. This is something that can have very serious consequences in a truck.

    Also, sometimes overdimensional or overweight permitted loads sometimes need to use these ramps to get around a low clearance, or weight limited bridge.

    2. The angle of the roadways shown is insufficient to give a semi truck adequate visibility to the right to safely make the left turn.

    I’ve emailed the designer with these concerns, and also gave him the link to this post. It’ll be interesting to see his response.

    td

  4. Joe Crumley says:
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    That’s a great link, td. And great observations. the lack of a straight shot from the off to the on ramp would make it a real pain for us car drivers, but a huge reasons for trucks to avoid. Much like the exits that have no entrances going the same direction.

    I was also impressed at the huge cost-savings they claim here: http://www.divergingdiamond.com/benefits.html

    Thanks for reading!

  5. Truckie D says:
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    I got a nice email reply. I had a couple more observations and questions. When I get the whole story sorted out, I’ll either post it here (space permitting) or put it in my blog with a link here.

    td

  6. Joe Crumley says:
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    Great. I look forward to reading the comments of the designer, Gilbert Chlewicki!

    I’m especially wondering how this implementation rates on his preference scale. On the site, http://www.divergingdiamond.com/articles.html, he makes it very clear that it is very important to get the first job in an area right. He says: “The ideal first location is a place where drivers will immediately and consistently see the benefits of the new design. … a location that will be retrofitting an existing interchange with traffic issues. This is the best way for the community to see all the advantages to the DDI design immediately and quickly grow to like the design. It is also provides the biggest cost savings possible.”

    “The first DDI in Springfield, Missouri is a great example. The DDI replaced a conventional diamond interchange that had backups that often stretched for miles. The instant success when the DDI opened was dramatic. There was also no need to replace or widen the existing bridge which made the cost savings for this project substantial. ”

    The St. Cloud sight doesn’t fit the bill. The traffic isn’t bad at that site, without any significant backups. Because it involves building a new bridge and digging the highway below grade, the expense is high. It may be perfectly suited for a DDE, but it doesn’t follow the designer’s preferences for a first implementation in an area.

  7. up arrow

    Thanks Joe for inviting me to your blog and posting some quick comments regarding your question about the ideal first location.

    Because I have not been to St. Cloud, I cannot speak specifically about the exact circumstances in your community. But knowing the few things I do know based on your blog comments, articles I have seen on this location, aerial maps on google, and speaking to some FHWA officials last week who are familiar with how DDIs are progressing in Minnesota, I should be able to address most of your question.

    First, it is my understanding that the St. Cloud location may not be the first DDI in the state of Minnesota. There are a few other locations that are looking into the DDI and it might be a matter of funding on which one gets built first.

    Second, in terms of how ideal this location is as a “first” location, we should probably break it down into several categories.

    Safety – Safety should be dramatically improved in this location. Grade separation almost always improves safety since there are less points of conflicts. And the DDI is considered a very safe interchange alternative. So in terms of safety improvements, it probably ranks 9 out of 10 if the collision rate at this location is average. 10 out of 10 if this was a high collision location.

    Operations – Traffic operations will definitely improve with a grade separation. Route 15 will be free flowing, so no more traffic signals. Stearns County Road will have have very short waits at the traffic signal versus what I am guessing is at least a one to two minute wait normally. It also looks like Route 15 was designed to eventually become a full highway with no signals. This project may be just one element of the whole story.

    I would say that the nice thing about this as a “first” is that you will see traffic improvements on all the roadways of the interchange, where on other DDI projects you often just see an improvement on the cross road of the highway. The final grade is up to you based on the traffic that is currently out there, but seeing traffic improve for everyone should be taken into account.

    Costs – You won’t see as big of a cost savings with a new interchange versus a retrofit, where the cost savings can sometimes be between 70-90% of other interchange options. But I am guessing that other interchange options probably had an estimated cost of between $20-$25 million. So this design will likely only see a 15-30% reduction of cost. That is still significant. I think as long as the option isn’t more expense than another option, then it is pretty good on the “first DDI” scale. But if you think doing nothing is a better alternative, the DDI will score low just like any other interchange alternative.

    Location – This location likely gets high marks, because I am guessing that this is a route that locals are very familiar with and don’t get many outsiders coming to this area. Drivers will become familiar with the DDI very quickly. Locations that may not be the most ideal first location are in places where there will be a lot of unfamiliar drivers, like near an airport or in a location where a significant amount of long-distance travelers will be using the exit. This location appears to be an area where mainly locals will be using it.

    I would conclude that even though this location might not be as perfect of a location for the “first” as the Springfield one, it still has many great qualities if indeed this becomes the first DDI in the state. The most important thing is that the first DDI be a success. If it is designed and constructed correctly, you should be very happy with your DDI, and in the end that is really what matters. Once you see how well the design performs, it will encourage more DDIs to be considered.

  8. Joe Crumley says:
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    Thanks so much for your expert comments. (Folks, he originated this design in this hemisphere!)

    A few thoughts:

    “Safety – Safety should be dramatically improved…” No argument there. Although my non-scientific anecdotal impression as an injury lawyer 3 miles away, it’s NOT CLOSE to being the most dangerous intersection in the area.

    “Traffic operations will definitely improve” Again, no argument, although I’m unaware of an inordinate delay there.

    “…looks like Route 15 was designed to eventually become a full highway with no signals” Absolutely true, and important (see below).

    “…I am guessing that this is a route that locals are very familiar with and don’t get many outsiders coming to this area.” I’m not so sure this is correct. Note that since Interstate 94 parallels the Mississippi, there are limited crossovers for traffic from Northern and Central Minnesota to access that major artery. Minn. Highway 15 serves that function, funneling much traffic from the north (US 10 in particular)through St. Cloud to the interstate.

    Also, the highway also passes through St. Cloud’s largest medical area (right at the new intersection) and also the large shopping area to the south. As such, large numbers of Northern and Central Minnesota travelers will first encounter this intersection on a rare medical visit or Christmas shopping trip.

    I certainly hope you’re right about this intersection!

    Did you see Truckie D’s (our favorite blogging over-the-road semi operator) questions above? I’m sure he’d appreciate your responses to his unique point of view.

  9. Truckie D says:
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    Ok InjuryBoard readers. I finally got a little free time to be able to follow up on this story.

    Here, I’ll just say that I’m firmly opposed to the widespread implementation of the DDI, particularly on the Interstate highway system, for a number of reasons. Due to the length, I’ve put it as a post to my blog at: http://truckied.wordpress.com/2011/03/21/the-diverging-diamond-interchange/

    As always, comments and questions are welcome.

    td